With development of the DC transmission and the renewable energy access grid technology in the world, an electronic power converter is applied more and more widely in the power system, with the continuous extension of application putting forward higher requirements for stable and dynamic performances of the converter. The traditional linear PID and PI controls cannot meet the requirements for the fast dynamic performance of the converter because of their characteristics of unclear control principle, complicated parameter setting and poor dynamic performance, wherein the traditional linear PID control has the following main problems:
1) The principle of the traditional PID control is as follows: The error of the given and feedback values is operated upon proportionally, integrally and differentially, and the resulting error value is compared with a triangle wave, thus obtaining a PWM signal of the switching device, with the output voltage adjusted by adjusting the pulse width of the PWM signal in each cycle. Thereby a modulation error is inevitably produced, resulting in a large waveform distortion as a direct result. Besides, lack of the mathematical derivation makes it impossible to know how PID works in the control process, which results in unclear control principle and inconvenient error investigation.
2) With design of the PID controller relying on precise mathematical model of the control system, typically the PID parameters are complicated to adjust and mostly set according to experience, which cannot guarantee optimality of the parameters; besides, lack of the self-setting capacity makes the PID parameters have to be constantly reset with the change of the control system parameters.
3) Improvement of efficiency and dynamic performance has become the development trend of the converter, while the strong coupling and nonlinear characteristics of the converter disenable the traditional linear feedback control to achieve satisfactory results, especially dynamic response and robustness, due to restrictions on bandwidth and feedback delay.
In addition, in the electronic power converters, due to the shortcoming of a traditional inverter that it has a through bridge arm and cannot be boosted, some researchers do research and make practical application design on a DC-DC combined inverter in recent years. The research shows that such a new combined inverter can achieve higher stable-state accuracy, a work approach more easily to be controlled, and also a more stable inverter system. With widely application of this inverter, research on the performance improvement of the DC-DC converter becomes more meaningful.
In the disclosed patent documents, there is no method yet of improving the dynamic performance of the converter from the control approach. In the disclosed journals and conference papers, many researchers conducted wide research on how to improve the dynamic response of the converter and the capacity of inhibiting interference and even jump of the input voltage and load current, and proposed a number of methods and achieved certain results, but these methods still have certain problems.
It was proposed in the literature to improve the dynamic response of the converter by adding a compensation circuit, which reduces the output voltage drop and shortens the dynamic response time to some extent, but needs an additional circuit and increases complexity of the converter. It was also proposed in the literature to shorten the dynamic response time of the converter by the digital control method “static model reference”; however, the research shows that the “static model reference” is more suitable for eliminating a stable-state error, and has an unobvious result in a dynamic process. It was also proposed in the literature to improve the dynamic response of the converter by keeping the charge-discharge balance of a capacitor; however, calculation of charging and discharging the capacitor is relatively complicated and has high accuracy requirements. Besides, an energy pulse modulation mode was also proposed in the literature, wherein by calculating the energy needed by the converter, the energy stored in an inductor is made to be able to provide the energy needed by the converter so as to attain the purpose of controlling the converter; however, the continuous current mode (CCM) and the discontinuous current mode (DCM) of the inductor need to be judged and controlled in the control process, respectively, in CCM the control derivation is more complicated because the inductor has some initial energy, and this method is only applicable to the Buck-Boost converter and the combined circuit thereof and needs to consider the initial energy of the inductor in other circuits such as Buck and Boost circuits, which will make the control derivation very complicated.
Besides, there are also some methods that improve the dynamic performance without sacrificing the stable-state accuracy by using two different control approaches in the stable state and transient state. Although these methods are effective, they are not easy to implement due to two sets of controllers used in the system, with smooth transition between the two sets of controllers being a huge challenge.
Therefore, it has become an important subject of the current research to provide a precise mathematical model having clear control principle and not relying on the control system, and a control approach having stronger robustness, faster dynamic response and good capacity of inhibiting disturbance of the input voltage and load.